The invention relates to a hydraulic consumer which comprises an arrangement of switching valves and check valves, and which permits selective connection of the consumer to a medium pressure line or a high pressure line. The selection of the lines may be controlled in an arbitrary or system-dependent manner, for example, by sensors.
It is common practice that such a hydraulic consumer is preceded by a hydraulically biased two-way valve in the consumer line, to which the high pressure line is applied on the one hand and the medium pressure line on the other hand. The hydraulically biased two-way valve ensures that the consumer line always receives the higher pressure, and that the connection from higher pressure to lower pressure is blocked.
The connection to lines which conduct differently high pressures, can be useful especially when the hydraulic consumer is a machine that has to meet different requirements. This applies in particular to hydraulic cylinder-piston units, which are used in mine development devices for supporting the shields in mining. Such mine development devices operate under a very high pressure. It is known to switch these mine development devices, for example, from a pressure of 300 bars to a pressure, hereafter medium pressure, of more than 300 bars. In this connection, the lower pressure is needed primarily for robbing and advancing the mine supports, as well as in the first phase of the setting step, when large volume flows must be switched (robbing=releasing and withdrawing the development unit; advancing=forward movement of the development unit; setting=positioning the development unit and its shields in the holding position). However, a high pressure is by all means avoided in the case of high volume flows because of the very great stress on the valves that is associated therewith. Primarily, however, the connection of high pressure in the operating phases, which proceed with a high volume flow, would lead to a collapse of the high pressure system.
It is therefore an object of the invention to improve the hydraulic consumer such that it can be applied to a medium pressure or a high pressure selectively, i.e., in an arbitrary or system-controlled manner, without risking a collapse of the high pressure source and the high pressure system, and without delivering large volume flows under a high pressure.